with%dr.%van%buskirk%%%

Transcription

1 with%dr.%van%buskirk%%%

2 How$to$do$well?$ Before$class:$read$the$corresponding$chapter$ Come$to$class$ready$to$par9cipate$in$Top$Hat$ Don t$miss$an$exam!!!!!!!!!!!!!!!!!!!!!!!!!!$

3 But$I m$not$good$with$science $

4 The$Scien9fic$Method$ not$just$for$scien9sts!$ you$use$it$almost$every$day$ Example:% my$computer$won t$start $ $ $ $ $ $ $Observa9on$ It$won t$start$because$the$bakery$is$dead $ $ $Hypothesis$ if$i$plug$it$in,$then$it$will$start $ $ $ $ $ $Predic9on$ (you$plug$it$in,$but$it$doesn t$start) $ $ $ $ $Test$ OK,$that$wasn t$the$problem $ $ $ $ $ $Reject$hypothesis$ maybe$the$power$bukon$response$is$impaired $ $Alternate$Hypothesis$ if$i$do$an$smc$reset,$then$it$will$start $ $ $ $Predic9on$ (reset$smc,$press$power.$computer$starts)$$ $ $$ $Test$$ Ah,$looks$like$that$was$it! $ $ $ $ $ $ $Do$not$reject$hypothesis$

5 another$ Do$not$reject$ hypothesis$ Observa9on$ Hypothesis$ Predic9on$ Test$ Think$of$alterna9ve$ Reject$ hypothesis$

6 another$ Do$not$reject$ hypothesis$ computer%won t%start% Observa9on(s)$ Hypothesis$ Predic9on$ Test$ Think$of$alterna9ve$ Reject$ hypothesis$ BIOL$100$

7 another$ Do$not$reject$ hypothesis$ It$won t$start$because% the$bakery$is$dead$ Observa9on(s)$ Hypothesis$ Predic9on$ Test$ Think$of$alterna9ve$ Reject$ hypothesis$ BIOL$100$

8 What constitutes a scientific hypothesis? It%is%based%on%observa>ons% It%proposes%an%explana>on%% It%must%be%testable% %% If%your%hypothesis%is%not%testable%% then%it%is%not%a%scien>fic%hypothesis.%

9 another$ Do$not$reject$ hypothesis$ Observa9on(s)$ Hypothesis$ Predic9on$ Test$ if$i$plug$it$in,$$ then$it$will$start$ Think$of$alterna9ve$ Reject$ hypothesis$ BIOL$100$

10 another$ Do$not$reject$ hypothesis$ Observa9on(s)$ Hypothesis$ Predic9on$ Test$ Think$of$alterna9ve$ Reject$ hypothesis$ BIOL$100$

11 What%cons>tutes%a% good%experiment?% Do$not$reject$ hypothesis$ Observa9on(s)$ Hypothesis$ Predic9on$ Test% Reject$ hypothesis$ BIOL$100$

12 The Good Experiment Tests the effect of one variable on the outcome Strives to minimize bias (of the subject and experimenter) Uses statistical analysis to estimate the significance of the result

13 % The%wellFcontrolled%experiment% % Tests%the%effect%of%one%variable%on%the%outcome% % Ideally,$you$create$two$groups$that$are$similar*$ then$ randomly$choose$which$group$will$get$the$treatment$ *Ideally$the$two$groups$will$be$well$matchedX$ If$the$average$age$of$each$group$is$similar,$you$have$ controlled $for$age$ If$the$average$exercise$level$is$similar,$you$have$ controlled $for$exercise$habits $ The%more%things%that%you%can% control %for,%the%bejerfdesigned%your%experiment%is.%

14 Types$of$variables$ What is the name of the variable that is manipulated during the experiment? What is the name of the variable that responds to the manipulation during the experiment?

15 The Good Experiment OK,$say$you$want$to$test$the$hypothesis$that:$ Vitamin%C%causes%increased%resistance%to%catching%colds % Is$it$beKer$that$you:$ a) Do$a$survey$to$ask$who$takes$Vitamin$C$and$how$o]en$they$catch$colds,$and$see$if$ there$is$a$rela9onship$between$vitamin$c$and$cold$resistance.$ b) Do$a$survey$to$ask$who$takes$Vitamin$C,$then$put$the$VitaminXtakers$into$one$ group$and$the$rest$into$another$group.$then$expose$each$group$to$a$mild$virus$ and$see$who$catches$cold;$note$difference$between$groups.$ c) Take$a$large$group$of$subjects$and$randomly$divide$them$into$two$groups.$Then$ have$one$group$take$vitamin$c$supplements$for$two$weeks.$then$expose$both$ groups$to$a$mild$virus$and$see$who$catches$cold;$note$difference$between$groups.$

16 The Good Experiment You%have%good%control%group.%Congratula>ons!% $ But$how$do$you$address$bias?$ $ 1) Subject/volunteer$bias$ 2) Experimenter/technician$bias$

17 The Good Experiment 1. Subject bias - Do you tell the subjects which group they are in? - What is it called when they don t know? - What do you give the control group?

18 The Good Experiment 2. Experimenter bias - What do you call an experiment in which neither the subjects nor the experimenter knows which group is which until after the data is collected?

19 The%wellFcontrolled%experiment% Tests%the%effect%of%one%variable%on%the%outcome% Strives%to%minimize%bias%(of$the$subject$and$experimenter)$ Uses%sta>s>cal%analysis%to%es>mate%the%significance%of%the%result% Why%do%we%need%sta>s>cs?% Because$there$is$certain$probability$that$a$difference$could$arise$ by%chance.$we$can$use$sta9s9cs$to$determine$this$probability.%

20 Sta9s9cs!$ Group%1% Group%2% %% heads %

21 Size$maKers!$ the number of subjects tested ( sample size ) the$size$of$the$difference$between$the$groups$ A large sample$size$and$a$large$difference = high statistical significance A small sample size and small difference = low statistical significance

22 Sta9s9cs$ 100$ %$of$subjects$with$colds$ 80$ 60$ 40$ 20$ 0$ 0$mg $$$1000$mg$ Is$this$difference$ sta's'cally* significant?%% or$just$due$to$ chance?$ Vitamin$C$consump9on$ (per$day)$

23 Sta9s9cs$ 100$ %$of$subjects$with$colds$ 80$ 60$ 40$ 20$ 0$ 0$mg $$$1000$mg$ Is$this$difference$ sta's'cally* significant?%% or$just$due$to$ chance?$ Vitamin$C$consump9on$ (per$day)$

24 The Good Experiment Tests the effect of one variable on the outcome Strives to minimize bias Uses statistical analysis to estimate the significance of the result

25 another$ Do$not$reject$ hypothesis$ Observa9on(s)$ Hypothesis$ Predic9on$ Test$ Think$of$alterna9ve$ Reject$ hypothesis$ BIOL$100$

26 If$a$hypothesis$stands$up$against$$ many$rounds$of$tes9ng,$$ it$can$become$a$theory.$ another$ Do$not$reject$ hypothesis$ Observa9on(s)$ Hypothesis$ Predic9on$ Test$ Think$of$alterna9ve$ Reject$ hypothesis$ BIOL$100$

27 What constitutes a theory? A$theory$is$a$hypothesis$$ (or$summary$of$a$group$of$hypotheses)$$ that$has$been$tested$extensively* and$has$not$(yet)$been$proven$wrong.$ Example:$ $ %The%Germ%Theory%of%Disease% % Can$you$think$of$others?$

28

29 Law$vs.$Theory$ A$$Law$summarizes$a$set$of$observa>ons.$ eg)$objects$fall$toward$the$earth,$the$posi>on$of$the$moon$affects$the$>des $ $The$Law$of$Gravity$ $objects$exert$an$akrac9onal$force$that$is$propor9onal$$ to$their$mass$and$inversely$propor9onal$to$the$distance$between$them.$ $$ ie)$gravity$exists$ $ A$Theory$summarizes$a$set$of$wellXtested$hypotheses.$ Einstein s$theory$of$general$rela9vity$explains$why$objects$exert$this$$ observed$force$$ $ ie)$why$gravity$exists.$ A$Law$is$NOT$a$ proven$theory.$there$is$no$such$thing$as$a$proven$theory!$ A$theory$is$the$highest$achievable$level$of$acceptance$in$science.$$ But$no$amount$of$tes9ng$can$ever$ prove $that$there$is$no$possible$alterna9ve.$

30 Using$Model$Organisms$ Can%be%very%informa>ve!%% Especially%useful%when%ethical%concerns%are%involved.%

31 Evalua9ng$Scien9fic$Informa9on$ Science$is$only$useful$if$we$share$it.$ $ How$do$we$communicate$our$work$to$other$scien9sts? To$nonXscien9sts?$ $ What$is$a$ primary $versus$a$ secondary $$ source$of$informa9on?$

32 ARTICLES 2007 Nature Publishing Group Epidermal growth factor signaling induces behavioral quiescence in Caenorhabditis elegans Cheryl Van Buskirk & Paul W Sternberg The epidermal growth factor receptor (EGFR)/ErbB receptor tyrosine kinases regulate several aspects of development, including the development of the mammalian nervous system. ErbB signaling also has physiological effects on neuronal function, with influences on synaptic plasticity and daily cycles of activity. However, little is known about the effectors of EGFR activation in neurons. Here we show that EGF signaling has a nondevelopmental effect on behavior in Caenorhabditis elegans. Ectopic expression of the EGF-like ligand LIN-3 at any stage induces a reversible cessation of feeding and locomotion. These effects are mediated by neuronal EGFR (also called LET-23) and phospholipase C c (PLC-c), diacylglycerol-binding proteins, and regulators of synaptic vesicle release. Activation of EGFR within a single neuron, ALA, is sufficient to induce a quiescent state. This pathway modulates the cessation of pharyngeal pumping and locomotion that normally occurs during the lethargus period that precedes larval molting. Our results reveal an evolutionarily conserved role for EGF signaling in the regulation of behavioral quiescence. In the mammalian nervous system, EGF signaling is involved in the proliferation and survival of glia as well as in neural migration and differentiation 1. In addition, neuronal EGFR/ErbB signaling has been linked to nondevelopmental events such as changes in synaptic plasticity 2,3 and the control of daily cycles of locomotor activity and feeding 4,5. At present, however, little is known about the effectors of ErbB signaling in neurons, much less the pathways that mediate the effects of EGF-related ligands on behavior. By contrast, much is known about the effectors of EGF signaling in non-neuronal cell types, in which activated EGFR has been shown to interact with multiple signaling pathways 6. The Ras-mitogen activated protein kinase (MAPK) pathway responds to EGFR activation by phosphorylating transcription factors, thereby affecting cell fates. Other signaling molecules that are activated in response to EGFR signaling include regulators of phospholipid metabolism such as PLC-g, which activates both Ca 2+ -dependent and protein kinase C (PKC)-dependent pathways, and phosphatidylinositol-3-oh kinase (PI(3)K), which influences cellular events such as proliferation, survival and adhesion. In the nematode C. elegans, the lin-3 and let-23 genes encode the sole EGF-like ligand and EGFR homolog, respectively 7,8 (Wormbase WS170). EGFR signaling through the Ras-MAPK pathway determines cell fates that affect viability as well as the development of the hermaphrodite vulva and male spicules 9. In addition, LET-23 acts through PLC-g and inositol-1,4,5-trisphosphate (Ins(1,4,5)P 3 ) signaling in the hermaphrodite spermatheca to regulate ovulation 10,11.No neuronal role has been described for LET-23. Here we report that overexpression of LIN-3, in addition to having effects on cell fate, causes a growth defect that is due to a reversible inhibition of feeding. Animals that overexpress LIN-3 also show severely decreased locomotion. These physiological effects of LIN-3 expression depend on the activities of neuronal LET-23 and PLC-g, and on the activities of several genes that are required for synaptic transmission (Supplementary Fig. 1 online). We show that the activation of EGFR specifically in the ALA neuron mediates the behavioral effects of LIN-3. In addition, we present evidence that worms with mutations in this pathway show inappropriate activity during the normally quiescent lethargus period that precedes larval molting. RESULTS LIN-3 expression inhibits feeding and locomotion C. elegans possesses a single EGF ligand and receptor pair, encoded by the genes lin-3 and let-23, respectively 7,8. LIN-3 overexpression during the L2 stage results in a multivulva (Muv) phenotype that results from hyperinduction of vulval fates 12, which depend on EGF signaling. During the course of our studies on the lin-3 splice variants (Supplementary Fig. 2 online), we observed that heat-shock-induced expression of LIN-3 caused animals to grow more slowly than heat-shocked control animals (Supplementary Table 1 online). This effect was elicited by three of the four LIN-3 isoforms (not shown) or by the LIN-3 EGF domain alone (Supplementary Table 1), and depended on the EGF receptor but not the Ras-MAPK or PI(3)K pathways (Supplementary Table 2 online). The growth defect occurred in response to a pulse of LIN-3 expression at any stage from hatching onward (Supplementary Table 1), making it unlikely to be due to a cell fate change and more likely to represent a physiological, rather than a developmental, growth defect. As the growth of C. elegans arrests in response to starvation 13, we analyzed the feeding behavior of animals in which LIN-3 expression Primary%Sources% $ original$data$ wriken$by$the$researchers$ peerxreviewed$ published$ Journal%Ar>cles% and% Published%Thesis%Work%

33 Other%secondary*sources:% $ Magazines$$ Newspaper$ar9cles$ Radio$stories$ InterviewsX$even$with$the$scien9st$who$ $$$$$$wrote$the$original$paperx$are$secondary$

34 Correla>on:$$ an$observed$rela'onship$between$two$$ variables$$(eg.$two$groups,$events,$condi9ons)$ Follows$the$PaKern:$ Condi>on%%%%(A)%%o^en%coincides%with%% an%(increase/decrease)%in%condi>on%%%%(b)%%%.% % or$ $ People%who%%%%%%%%(A)%%%%%%%%%are%(more/less)%likely%to%%%%%%%%(B)%%%%%%%.% BIOL$100$

35 Correla9on$/$Causa9on$ Correla>on:% The%populariza>on%of%rap%music%in%the%late%1980s%coincided%% %%with%a%sharp%rise%in%narco>cs%use%and%violent%crimes. % A% B% (songs%about% %drugs%and%violence)% (increase%in%drug%use% and%violent%crime)% (music$about$crime$can$cause$criminal$behavior)$ BIOL$100$

36 Correla9on$/$Causa9on$ Correla>on:% The%populariza>on%of%rap%music%in%the%late%1980s%coincided%% %%with%a%sharp%rise%in%narco>cs%use%and%violent%crimes. % A% B% (songs%about% %drugs%and%violence)% (increase%in%drug%use% and%violent%crime)% increased$crime$causes$more$songs$to$be$wriken$about$crime$ (people$tend$to$sing$about$things$that$are$going$on$around$them)$ BIOL$100$

37 Correla>on:% People$who$regularly$wear$seatbelts$are$ more$likely$to$be$diagnosed$with$cancer$ than$those$who$do$not$wear$seatbelts. $ What%do%you%make%of%this?% Does%this%mean%that%seatbelts%cause%cancer?% BIOL$100$

38 Correla9on$/$Causa9on$ C% (live%longer)% A% B% (wear%seatbelt)% (cancer)% BIOL$100$ Do%seatbelts%cause%cancer?%No.%In%fact%there%is%no%correla>on%IF%you%control%for%age.%

39 A% B% correlates%with% A% B% A% B% C% A% B% There%are%many%possible%explana>ons!%

40 The$Correla9on/Causa9on$Song$ by$alan$reifman$ (to$the$tune$of$the$beatles $Revolu>on)$ $$ You%say%you've%got%a%correla>on,% Well,%you%know,%it%says%nothing%about%cause.% You've%got%to%do%experimenta>on,% Well,%you%know,%to%fulfill%science's%laws.% With*a*correla'on*between*B*and*A,* Causal*direc'on*could*go*either*way,$ $ You%say%you've%got%a%correla>on,% Well,%you%know,%A%and%B%are%only%linked,% You%need%further%inves>ga>on,% Well,%you%know,%to%show%the%pathway%you%think.% There's*another*op'on,*and*this*is*key,* There*could*be*a*third*variable*called*C.* A%correla>on%cannot%be% Air>ght!% Air>ght!!% Air>ght!!!% A%correla>on%cannot%be% Air>ght!% Air>ght!!% Air>ght!!!%